In-line type electron gun

ABSTRACT

An in-line electron gun is constructed according to the present invention such that the common center axes (18b), (18c) of side beam apertures (16b), (16c) of a control electrode (12) and an accelerating electrode (13) are displaced toward a tube axis (19) from the center axes (21b), (21c) of the side beam apertures defined in the end surface of the focussing electrode (14) on the side of the accelerating electrode, and the common center axes (24b), (24c) of the side beam apertures (23b), (23c) defined in the opposite end surfaces of the focussing electrode (14) and the anode electrode (15) are displaced toward the tube axis (19) from the common center axes (18b), (18c) of the side beam apertures (16b), (16c) of the control electrode (12) and the accelerating electrode (13).

TECHNICAL FIELD

The present invention relates to an in-line electron gun built in acolor picture tube.

BACKGROUND ART

Generally, in a color picture tube comprising an in-line type electrongun from which three electron-beams are emitted into a plane, as shownin FIG. 1, a center beam 1a and side beams 1b, 1c pass through mainlenses 2a, 2b, 2c, respectively, to be focussed. In order that the sidebeams 1b, 1c are converged to a point 3 at the center of the phosphorscreen together with the center beam 1a, a beam convergence angle θ isgiven between each of the side beams 1b, 1c and the center beam 1a.Also, a self-convergence deflection magnetic field is provided so thatthe convergence of the three beams 1a, 1b, 1c is performed automaticallyeven at deflection to the peripheries of the screen. In the picture tubesystem thus constructed, the beam convergence angle θ affects the beamconvergence characteristics over the entire phosphor screen.

The beam convergence angle θ can be given by arranging three electronguns obliquely. But, in that method, the beam convergence angle θ isliable to be varied by assembly errors that occur when the threeindependent electron guns are integrated into an assembled gun.Generally, therefore, a unitized electron gun structure in which therelative displacement of the three electron beams is expected to besmall is employed as shown in FIG. 2. A unitized electron gun isdescribed in detail in Japanese Patent Publication No. 4905/77 andothers. The center axes 6b, 6c of the side beam apertures 5b, 5c amongthe beam apertures 5a, 5b, 5c at the end of a focussing electrode 4 onthe side of an anode electrode, and the center axes 9b, 9c of the sidebeam apertures 8b, 8c among the beam apertures 8a, 8b, 8c at the end ofthe anode electrode 7 on the side of the focussing electrode aredisplaced or offset to each other to obtain axially asymmetric side mainlenses 10b, 10c, so that the side beams are electrostatically deflectedby the beam convergence angle θ.

Incidentally, in this unitized electron gun structure, the beamconvergence angle θ is determined by the relative positions of the sidebeam apertures 5b, 5c of the focussing electrode 4 and the side beamsapertures 8b, 8c of the anode electrode 7, and therefore a very severemanufacturing accuracy is required for the electrodes 4 and 7.

SUMMARY OF THE INVENTION

In the in-line type electron gun according to the present invention, thecenter axis common to the respective side beam apertures of the controlelectrode and the accelerating electrode is offset toward the tube axisfrom the center axis of the side beam aperture of the focussingelectrode end surface on the side of the accelerating electrode, and atthe same time, the center axis common to the respective side beamapertures at the opposite side surfaces of the focussing electrode andthe anode electrode is offset toward the tube axis from the center axiscommon to the respective side beam apertures of the control electrodeand the accelerating electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for explaining the convergence of three electronbeams by a conventional in-line type electron gun,

FIG. 2 is a side sectional view showing the electrode configuration of apart of the same electron gun,

FIG. 3 is a side sectional view of an in-line type electron gunembodying the present invention, and

FIG. 4 is a diagram for explaining the convergence of three electronbeams from the electron gun shown in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the preferred embodiment of the invention shown in FIG. 3, threecathode electrodes 11a, 11b, 11c, arranged on a horizontal straightline, a control electrode 12, an accelerating electrode 13, a focussingelectrode 14 and an anode electrode 15 make up a unitized in-lineelectron gun. A center beam aperture 16a and side beam apertures 16b,16c of the control electrode 12 share common central axes 18a, 18b, 18crespectively with a center beam aperture 17a and side beam apertures17b, 17c of the accelerating electrode 13. The center axis 18a common tothe center beam apertures 16a and 17a is coaxial with the tube axis 19.

As shown in FIG. 3, the anode electrode 15 preferably is a cup shapedmember provided in its end surface with a center beam aperture 23a andside beam apertures 23b and 23c, and the focusing electrode 14preferably is a composite member formed of two axially joined cup-shapedmembers, each provided in its end surface with respective center andside beam apertures 20a, 20b, 20c (which are disposed opposite the beamapertures 17a, 17b and 17c, respectively, of the accelerating electrode13) and 22a, 22b, 22c (which are disposed opposite the beam apertures22a, 22b, 22c, respectively, of the anode electrode 15). As shown, theone of the the cup-shaped members of the focusing electrode 14 whose endsurface faces, i.e. is opposite, the end surface of the anode electrode15 is of the same size and shape as the anode electrode 15.

The center axis 21a of the center beam aperture of the focussingelectrode 14 on the side of the accelerating electrode 13, is coaxialwith the tube axis 19. However, the center axes 21b, 21c of the sidebeam apertures 20b, 20c respectively are displaced from theabove-mentioned common center axes 18b, 18c respectively. In otherwords, the common center axes 18b, 18c for the side beam apertures 16b,16c, 17b, 17c of the control electrode 12 and the accelerating electrode13 respectively are offset toward the tube axis from the center axes21b, 21c of the side beam apertures 20b, 20c of the focussing electrode14 on the side of the accelerating electrode 13.

Further, the center beam aperture 22a and the side beam apertures 22b,22c of the focussing electrode 14 on the side of the final acceleratingelectrode 15 share common center axes 24a, 24b, 24c respectively withthe center beam aperture 23a, and the side beam apertures 23b, 23c ofthe final accelerating electrode 15 on the side of the focussingelectrode. The common center axis 24a for the center beam apertures 22a,23a is coaxial with the tube axis 19, while the common center axes 24b,24c for the side beam apertures 22b, 22c, 23b, 23c respectively areoffset toward the tube axis from the common center axes 18b, 18crespectively.

In the in-line electron gun constructed in this way, an axiallysymmetric prefocus lens electric field is formed between the center beamaperture 17a of the accelerating electrode 13 and the center beamaperture 20a of the focussing electrode 14, while axially-asymmetricprefocus lens electric fields are formed between the side beam apertures17b, 17c of the accelerating electrode 13 and the side beam apertures20b, 20c of the focussing electrode 14 respectively. As a result, thethree electron beams generated from the three cathode electrodes 11a,11b, 11c and passed through the center beam aperture 16a and the sidebeam apertures 16b, 16c of the control electrode 12 are pre-focussed bysaid prefocus lens electric fields. Since the both side prefocus lenselectric fields are axially asymmetric, the side beams are deflectedslightly toward the tube axis.

FIG. 4 shows three prefocus lens sections as equivalent electron sources25a, 25b, 25c. The equivalent electron sources 25b, 25c on the bothsides are displaced from the above-mentioned common center axes 24b, 24crespectively by Δx. The center beam 26a advances straight along the tubeaxis 19 and enters the axially-symmetric center main lens 27a on thetube axis 19, while the side beams 26b, 26c advance obliquely at anangle of α and enter the axially-symmetric side main lenses 27b, 27c.

The center beam 26a and the side beams 26b, 26c are focussedrespectively by the main lenses 27a, 27b, 27c, and in the absence of thedeflection magnetic field acting thereon, the side beams 26b, 26c arebiased by Δx·M from the center axes 24b, 24c on the phosphor screen 28.M indicates the lens magnification.

Therefore, when the center displacement Δx is set so that the biasamount (Δx·M) is equal to the distance S between the center axes 24b,24c and the tube axis 19 (Δx·M=S), the center beam 26a and the sidebeams 26b, 26c can be converged to a point at the center on the phosphorscreen 28.

The prefocus lenses on both sides 26b, 26c are axially asymmetric. Ifthe respective amounts of displacement of the center axes 18b, 18c fromthe center axes 21b, 21c are appropriately set to provide an appropriateinclination angle α, the beam spot (bright spot) on the phosphor screen28 can be made a true circle. Also, since the center axes of theassociated beam apertures 22 and 23 on the respective opposed or facingside ends of the focussing electrode 14 and on the final acceleratingelectrode 15 are not required to be displaced from each other, the halfof the focussing electrode 14 facing the final accelerating electrode oranode 15 can be formed in the same press die used for forming the finalaccelerating electrode 15. Thus convergence failures caused byvariations in the shape of the electrodes 14, 15 can be reduced.Further, even when a satisfactory roundness of the beam apertures cannotbe obtained due to the natures inherent to the press die, at least theopposite side ends of the electrodes 14, 15 can be reversely combined intheir upper and lower relation, and therefore a superior beam spot shapewith a high uniformity of convergence can be obtained.

INDUSTRIAL APPLICABILITY

As explained above, the in-line electron gun according to the presentinvention facilitates the manufacture, management and assembly of thefocussing electrode and final accelerating electrode of comparativelycomplicated construction, thus producing a superior beam spot shape,that is, a high-resolution characteristic.

We claim:
 1. In an in-line electron gun for producing a center beam andside beams which is enclosed in a tube having a main tube axis, withsaid gun including a plurality of cathodes, and serially arrangedcontrol, accelerating, focussing and anode electrodes for said cathodes,and with each said electrode having a center beam aperture, whoserespective center axes are all aligned with said tube axis, and havingside beam apertures whose respective center axes are all parallel tosaid tube axis, the improvement wherein for each side beam: the sidebeam aperture of said control electrode and of said acceleratingelectrode have a common center axis which is displaced toward the tubeaxis from the center axis of the side beam aperture defined in the endsurface of said focussing electrode on the side of said acceleratingelectrode; and the associated side beam apertures respectively definedin the opposed end surfaces of said focussing electrode and said anodeelectrode have the same diameter, and have a common center axis which isdisplaced toward the tube axis from said common center axis of the sidebeam apertures of said control electrode and said acceleratingelectrode.
 2. An in-line electron gun enclosed in a tube and comprising:three cathode electrodes arranged in a straight line, a controlelectrode, an accelerating electrode, a focussing electrode and an anodeelectrode; each of said control electrode, said accelerating electrode,said focussing electrode and said anode electrode having a center beamaperture and side beam apertures; the common center axis of therespective side beam apertures of said control electrode and saidaccelerating electrode being displaced toward the tube axis from thecenter axis of the side beam apertures defined in the end surface ofsaid focussing electrode on the side of said accelerating electrode; andthe associated side beam apertures respectively defined in the opposedend surfaces of said focussing electrode and said anode electrode have acommon center axis which is displaced toward the tube axis from thecommon center axis of the respective side beam apertures of said controlelectrode and said accelerating electrode.
 3. An in-line electron gunenclosed in a tube and comprising: three cathode electrodes arranged ina straight line, a control electrode, an accelerating electrode, afocussing electrode and an anode electrode; said focussing electrodeincluding a first cup-shaped member of the same size and shape as saidanode electrode and positioned on the side of the same and a secondcup-shaped member positioned on the side of said accelerating electrode,the common center axis of each side beam aperture of said controlelectrode and said accelerating electrode being displaced toward thetube axis from the center axis of a side beam aperture of the secondcup-shaped member end surface of said focussing electrode, and thecommon center axis of the side beam apertures respectively defined inthe opposed end-surfaces of said anode electrode and said first cupshaped member being displaced toward the tube axis from the common axisof the respective side beam apertures of said control electrode and saidaccelerating electrode.
 4. An in-line electron gun according to claim 3,characterized in that said first cup-shaped member and said anodeelectrode are each formed by mold pressing using a common die.
 5. Anin-line electron gun according to claim 1, wherein a relation S=Δx·Mholds where Δx designates the distance of displacement between thecenter axis of a prefocus lens formed by the respective side beamapertures of said control electrode and said accelerating electrode andthe common center axis of the respective side beams of said focussingelectrode and said anode electrode, S designates the inter-axis distancebetween the center axis of the center beam and said common center axisof the respective side beams, and M designates the magnification of amain lens formed by said focussing electrode and said anode electrode.6. An in-line electron gun according to claim 2, wherein a relationS=Δx·M holds where Δx designates the distance of displacement betweenthe center axis of a prefocus lens formed by the respective side beamapertures of said control electrode and said accelerating electrode andthe common center axis of the respective side beams of said focussingelectrode and said anode electrode, S designates the inter-axis distancebetween the center axis of the center beam and said common center axisof the respective side beams, and M designates the magnification of amain lens formed by said focussing electrode and said anode electrode.7. An in-line electron gun according to claim 3, wherein a relationS=Δx·M holds where Δx designates the distance of displacement betweenthe center axis of a prefocus lens formed by the respective side beamapertures of said control electrode and said accelerating electrode andthe common center axis of the respective side beams of said focussingelectrode and said anode electrode, S designates the inter-axis distancebetween the center axis of the center beam and said common center axisof the respective side beams, and M designates the magnification of amain lens formed by said focussing electrode and said anode electrode.8. An in-line electron gun according to claim 2 wherein said associatedside beam apertures of said focussing electrode and of said anodeelectrode are of the same diameter.